Conventional series-regulated linear power supplies are regulated by varying their resistance to cope with input voltage changes or load current demand changes. The linear regulator can, therefore, tend to be very inefficient. A switch-mode power supply, however, uses a high frequency switch (in practice a transistor) with varying duty cycle to maintain the output voltage. Output voltage variations caused by the switching action are typically filtered out using inductive and/or capacitive filter arrangements. Many modern power supplies and power converters utilize switch-mode topologies due to their typically high efficiency. Another advantage of switch-mode topologies is lower system weight in comparison to linear topologies, the reduction in weight being due to smaller magnetics associated with the high switching frequency of switch-mode systems.
In switch-mode technology, it is very important to ensure that the active devices (i.e., transistor power switches) remain within their safe operating area (SOA). This limitation can generally be addressed in several ways. One way is soft-switch technology with zero-current switching (ZCS) and zero voltage switching (ZVS). Another way is to implement snubber circuits, which control the “load line” of power devices. Yet another way is over-rating the device sufficiently to stay within its SOA.
“Snubber” circuits are often incorporated into switch-mode power converters to suppress voltage transients generated by the switching circuitry of the converter. However, available snubber circuits have significant disadvantages. The first disadvantage is power consumption, which may be as much as 2-3% of the nominal power of the converter. Further, they cannot work with a simple full leg power conversion stage (i.e., a half-bridge configuration). Adding more components, for example, soft-switch technology with auxiliary power switching, may resolve these problems. However, this approach has disadvantages in that it adds to the cost and complexity of the system. There is a need for a more efficient snubber for use with switch-mode power converters.